Knight tour, using a generator

knight_tour1.py

#!/usr/bin/env python3

''' Knight tour, using recursive backtracking
    Version using a generator in a class

    Written by PM 2Ring 2018.05.27
'''

class Board:
    def __init__(self, size):
        self.board = [[0] * size for _ in range(size)]

    def __repr__(self):
        return '\n'.join([' '.join([f'{u:>2}' for u in row])
            for row in self.board])

    def __setitem__(self, yx, val):
        y, x = yx
        self.board[y][x] = val

    def __getitem__(self, yx):
        y, x = yx
        return self.board[y][x]

class KnightTour:
    moves = ((-2, -1), (-2, 1), (-1, -2), (-1, 2), 
        (1, -2), (1, 2), (2, -1), (2, 1))

    def __init__(self, size, cy=0, cx=0):
        self.size = size
        self.hinum = size * size
        self.board = Board(size)
        self.cy = cy
        self.cx = cx

    def __iter__(self):
        cy, cx = self.cy, self.cx
        self.board[cy, cx] = 1
        yield from self.solve(cy, cx, 2)

    def solve(self, cy, cx, n):
        size = self.size
        board = self.board
        if n > self.hinum:
            yield board
        else:
            for mx, my in self.moves:
                y, x = cy + my, cx + mx
                if 0 <= y < size and 0 <= x < size and not board[y, x]:
                    board[y, x] = n
                    yield from self.solve(y, x, n + 1)
                    board[y, x] = 0

if __name__ == '__main__':
    import sys

    size = int(sys.argv[1]) if len(sys.argv) > 1 else 5
    cy = int(sys.argv[2]) if len(sys.argv) > 2 else 0
    cx = int(sys.argv[3]) if len(sys.argv) > 3 else 0
    # We should check that 0 < size and 0 <= cy < size and 0 <= cx < size

    for i, b in enumerate(KnightTour(size, cy, cx), 1):
        print(i, b, sep='\n', end='\n\n')